1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine.
2. Description of the Prior Art
A protective device for a copying machine known in the art is provided aiming at operating in an obviously abnormal state, such as when the exposure lamp for an original manuscript is continuously illuminated. One of such protective devices is so constructed as to detect an abnormal temperature around the exposure lamp to thereby protect it. In the copying machine with such a protective device, a problem arises, therefore, that the protective device does operate until the temperature rises to a substantially large one.
Furthermore, after detecting a continuous illumination, in order to precisely set a time period during which the protective device operates, it is required to provide a pulse oscillator for supplying pulses to a counter which measures the time period, a circuit for starting and stopping the operation of the counter, and similar complicated circuits. Therefore, some disadvantages arise that the reliability of the protective device is degraded and that the device becomes expensive.
In an image forming apparatus having a size change function, an image to be formed from an original manuscript may be required to reduce in size only in the scanning direction on the original. In this case, as is similar to the case wherein the size in both vertical and lateral directions of the original is reduced by the same reduction ratio, an image can be obtained whose size is reduced only in the scanning direction of the original, by setting a reduction ratio in the scanning direction alone. However, in this case, since a timing (registration timing) for feeding a recording medium to the image forming apparatus is set identically with that of the preset reduction mode, there arises a problem that an image is formed to be biased in position in the transporting direction of the recording medium.